1. Field of the Invention
Nanofiber structures and methods for producing nanofiber structures having surface porosity and coating methods for porous and non-porous nanofibers. These materials may be used in applications such as catalysis, lighting, and nanomaterial storage and transportation.
2. Description of the Related Art
Nanofibers can be used in a variety of applications from clothing industry to military combat. Electrospinning techniques for nanofiber production have attracted attention recently. The unique material properties of nanofiber materials mainly come from the ultra-high surface area. Nanofibers with porous surface feature have higher surface area than smooth nanofibers. Several types of fabrication methods had been reported in the literature to make porous feature on nanofiber surface.
Template removal and fabrication of nanoporous inorganic nanofibers have been reported by electrospinning a blend solution of a polymer and silica nanoparticle followed by removal of the polymer by calcinations, leaving behind the silica nanofibers, as disclosed in Kanehata et. al., Nanotechnology. 2007, 18, 1-7. Porous polymer nanofibers have also been obtained by low temperature electrospinning using ice crystal as a removable template, as disclosed by Simonet et al., Polymer Engineering and Science, 2007, 47, 2020-2026. However, these methods involve either specific material processing condition or special electrospinning conditions to obtain the desired porous nanofiber structure. Other techniques have also been used to obtain porous nanofibers by spinning the fiber into water vapor, a technique based on the so called “breath figures.” Srinivasarao et. al. in Science, 292 (5514): 79 Apr. 6, 2001 have reported on porosity development in polymer membranes due to the deposition of minute droplets of water. This technique has the potential for electrospinning of porous nanofibers, as reported by S. Megelski, J. S. Stephans, D. B. Chase, and J. F Rabolt, in Macromolecules, 35, 8456 (2002). Wendroff et. al. (U.S. Pat. No. 6,790,528) also reported that, with specific polymer/volatile solvent pairs, conventional spinning can yield porous nanofibers.
U.S. application Ser. No. 11/559,260 entitled “Luminescence Device,” referenced above, describes ways to utilize nanoparticles and nanofibers to produce a white light spectrum.
One problem discussed in detail below and recognized by the inventors relates to the safety, handling, attachment, processing of nanoparticles in the luminescent device and catalysis applications. This general problem affects not only the luminescent applications but also affects other application areas where nanoparticle handling and/or attachment to other material structures is at issue. Other problems with the background art, which the present inventors have recognized, concern the lack of porosity control in these background art techniques.